The present invention relates to a plastic cap system with a base cap that can be installed on the neck of a container, with an outlet and a pour spout that is connected with this and is closed at one end, this serving as a sealing pin, and with a screw cap that is rotably connected with the base cap and having a central opening, into which, when the cap system is in the closed state, the upper closed end of the pour spout protrudes so as to form a seal. Such cap assemblies have been commercially available for many years, and have been used as caps for plastic containers, in particular as used for liquid soap and cosmetics. In this area of application, such cap assemblies have exhibited only a few disadvantages. Above all, the most significant problem is their poor sealing capability. The above cited cap assemblies as in the state of the art operate with a base cap that is fixed as the cap assembly is opened and closed, and a spout or pin that is rigidly connected to this, and a screw cap that can be moved vertically up and down in an axial direction, relative to the base cap. The seal between the base cap and the screw cap is effected, on the one hand, between the central spout on the base cap and the edge of the central opening in the screw cap when the cap assembly is in the closed state and, on the other hand, directly between the outer annular wall of the base cap or the container neck and the vertical annular wall of the screw cap. At the second cited location, the seal is effected mostly through the inside thread of the screw cap and the outside thread of the base cap or the container neck. In the open position of the cap assembly, in which the screw cap has been displaced upwards relative to the container neck, the threads engage each other only partially and the seal is thus imperfect. This is the result of the fact that the total space beneath the screw cap fills with the contents of the container and, when the cap assembly is closed, this has to be forced back into the container.
Plastic cap assemblies of this kind have not been used for foodstuffs, for these impose far greater demands for seal quality. Such containers are mostly sealed with aluminum foil. However, because cap assemblies with a sealing pin must be secured against twisting off, cap assemblies of this kind could not be used on sealed containers.